Malignant tachyarrhythmia, for example, ventricular fibrillation, is an uncoordinated contraction of the cardiac muscle of the ventricles in the heart, and is the most commonly identified arrhythmia in cardiac arrest patients. If this arrhythmia continues for more than a few seconds, it may result in cardiogenic shock and cessation of effective blood circulation. As a consequence, sudden cardiac death (SCD) may result in a matter of minutes.
In patients at high risk of ventricular fibrillation, the use of an implantable cardioverter-defibrillator (ICD) system has been shown to be beneficial at preventing SCD. An ICD system includes an ICD, which is a battery powered electrical shock device, that may include an electrical housing electrode (sometimes referred to as a can electrode), that is coupled to one or more electrical lead wires placed within the heart. If an arrhythmia is sensed, the ICD may send a pulse via the electrical lead wires to shock the heart and restore its normal rhythm. Owing to the inherent surgical risks in attaching and replacing electrical leads directly within or on the heart, subcutaneous ICD systems have been devised to provide shocks to the heart without placing electrical lead wires within the heart or attaching electrical wires directly to the heart.
Electrical leads being utilized in subcutaneous systems typically include a single dedicated defibrillation electrode and one or more dedicated pacing and/or sensing electrodes along the length of the lead. Each of these electrodes is electrically connected to separate conductors within the lead body and connected to the ICD. Thus, the capability of the electrical lead to deliver a defibrillation shock, a pacing pulse, or to sense a cardiac depolarization is fixed to the particular longitudinal or radial placement of each electrode.